Solar panels which convert radiant energy from sunlight directly into electricity are known as photovoltaics.
Hereby direct current is generated, and by connecting the modules in series a higher voltage can be reached. By means of an inverter this higher voltage is converted from DC into AC current of 50 Hz and fed into the grid.
For each kWh fed into the grid a certain compensation is being paid for 20 years according to the Renewable Energy Act. Photovoltaic systems are mainly installed on roofs or mounted in a good location with plenty of sunlight in the open field. For an installation in an open area such as a meadow or on a commercial space you get a lower feed-in tariff as for an installation on a roof.
Solarthermics refers to the use of solar thermal energy, i.e. the use of solar heat.
A solar thermal system consists essentially of a transparent cover, usually made of glass, a collector box and the absorber tubes. This absorber tubes are fixed to a metal plate, that converts sunlight into heat. The heat is transferred to the heat transfer fluid in the tubes, usually a water-glycol mixture.
On the back there is an insulator, so heat losses are minimized. A solar thermal system can heat the tap water or support the heating during the summer months.
A heating supported by a solar thermal plant may cover about 36% of the heat required in a residential house. To compensate for the day and night variations and to bridge cloudy days, a large thermal storage should be installed. *
* Source: V. Quaschning, Renewable Energy Systems, Hasner Verlag, 2009